mm/hwpoison: put page in already hwpoisoned case with MF_COUNT_INCREASED

In already hwpoisoned case, memory_failure() is supposed to return with
releasing the page refcount taken for error handling.  But currently the
refcount is not released when called with MF_COUNT_INCREASED, which makes
page refcount inconsistent.  This should be rare and non-critical, but it
might be inconvenient in testing (unpoison doesn't work).

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Naoya Horiguchi <[email protected]>
Suggested-by: Miaohe Lin <[email protected]>
Reviewed-by: Miaohe Lin <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: Yang Shi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/memory-failure.c

@@ -1811,6 +1811,8 @@ int memory_failure(unsigned long pfn, int flags)
 		res = -EHWPOISON;
 		if (flags & MF_ACTION_REQUIRED)
 			res = kill_accessing_process(current, pfn, flags);
+		if (flags & MF_COUNT_INCREASED)
+			put_page(p);
 		goto unlock_mutex;
 	}